DC to DC converters are used to convert an input DC voltage to an output DC voltage. Such converters may step down (buck) or step up (boost) the input DC voltage. One type of buck converter is a synchronous buck converter. This converter typically has a controller, driver, a pair of switches, and an LC filter coupled to the pair of switches. The controller provides a control signal to the driver which then drives the pair of switches, e.g., a high side switch and a low side switch. The driver alternately turns each switch ON and OFF thereby controlling inductor current and the output voltage of the DC to DC converter. Such controllers typically utilize a pulse width modulated signal to control the state of the high and low side switches.
In general, if the PWM signal is high, the high side switch is ON and the low side switch if OFF. This state of switches will be referred to herein as a “switch ON” state. In this state, the inductor is coupled to the input voltage source. In a buck converter, the input voltage is necessarily greater than the output voltage so there is a net positive voltage across the inductor in this switch ON state. Accordingly, the inductor current begins to ramp up. If the PWM signal is low, the high side switch is OFF and the low side switch is ON. This state of switches will be referred to as a “switch OFF” state. In a buck converter, there is a net negative voltage across the inductor in this state. Accordingly, the inductor current begins to ramp down during this low side switch OFF state. Hence, the pulse width of the PWM signal determines the time on for the switch ON state and the time off for the switch OFF state. Such pulse width may be adjusted by directly monitoring the inductor current level via a sense resistor or by comparing the output voltage with a reference voltage level.
Accordingly, there is a need in the art for a controller for a DC to DC converter that provides a PWM signal during a first time interval based on an input voltage to the DC to DC converter less a signal representative of the output voltage.